Articles that have been damped for sound can include some type of viscoelastic material applied to a vibratory article, such as an automotive component. The viscoelastic material absorbs and dissipates the vibrational energy generated by the article by converting mechanical energy associated with the vibrations into thermal energy that is dispersed within the sound damping material layer, and thus reduces the noise associated therewith. There are several different structures commonly used for sound damping purposes, including: free-layer structures, constrained-layer structures, and laminates.
Free-layer structures are structures where a sound damping viscoelastic material by itself is applied to the surface of a vibratory article. In such an arrangement, vibratory or acoustical energy created by a noise or vibration source on one side of the article is dissipated in the adjacent viscoelastic layer so that it is attenuated. In the case of constrained-layer structures, the sound damping viscoelastic material may act as an adhesive and is sandwiched between the vibratory article and an additional rigid constraining layer. The vibration damping is generally due to relative movement between the vibratory article and the rigid constraining layer which causes a shearing movement in the viscoelastic material which translates into heat energy. Sound damping laminates perform much in the same way as constrained-layer structures, however the vibratory article includes a pair of thin constraining layers with a viscoelastic adhesive layer therebetween.